1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method which carry out a gamma correction for input data.
2. Description of the Related Art
In general, a display for a television or a car navigation system has such a property that a brightness (luminance) to be displayed does not emit a light in proportion to the intensity of a signal input. When the signal input is represented as x, a luminance y of a light emitting output is expressed in y=xγ and a nonlinear curve is obtained. Such a nonlinear characteristic is referred to as a gamma characteristic. In this case, a γ value varies depending on the type of the display. For example, a CRT has γ=2.2.
As a method of correctly carrying out a display operation by using a display, a correction of y=x1/γ is performed for video output signals R, G and B (signal input x). This is referred to as a gamma correction.
FIG. 6 is a chart showing a gamma correction curve in case of γ=2.2. The gamma correction curve is obtained by carrying out a normalization in such a manner that the value of gamma correction data y ranges from 0 to 255 when color data x are 8-bit data (0 to 255), and is calculated by the following equation.y={(x/256)1/2.2}×256
A related gamma correcting method includes a method of storing curve data for a gamma correction in a look-up table constituted by an RAM or an ROM and converting the same data or a method of carrying out a polygonal line approximation over a curve for the gamma correction (for example, see JP-A-3-139972).
In the related method using a look-up table, however, there are circumstances in which a look-up table having a large capacity is required and the scale of a circuit is increased when the number of the bits of input data is increased, that is, a gradation becomes finer. On the other hand, there are circumstances in which the scale of a circuit can be reduced, while picture quality is influenced if a great error is made between gamma correction data subjected to a polygonal line approximation and an ideal value in the method using the polygonal line approximation.